Google today announced its free Google Voice service is now open to everyone in the U.S. The online voicemail and telecommunications service already counts around 1 million people among its regular users, but until today it was available through invitation only, as Google wanted to hold off launching the service more widely until it was sure it had enough infrastructure in place to support a larger user base.

Google Voice gives users one number that can ring on all their phones – mobile, home and office for example – depending on the rules they set. It includes a bunch of useful and free features, such as transcribed voicemail sent as email or text message, conference calling, outbound domestic calls, and call-screening. International calls are also supported, for a fee, but they cost a fraction of what phone companies typically charge per minute. Alternatively, if you don't want a new phone number to deal with, Google Voice can be used with your existing line – albeit with limited functionality.

You can check out a brief explanation of the service in the Google-produced video above. Native apps for Android and Blackberry phones are available, while Palm Pre and iPhone users can use the HTML5 web-based app to use most of its features. A full-featured app for the iPhone was also developed, but Apple controversially rejected it last year on grounds that it duplicates functionality in the popular smartphone.